This invention relates to an improved process for the preparation of meta-aryloxy-benzaldehydes, these compounds being valuable intermediates, for example, in the preparation of pesticides containing a meta-aryloxy-benzyl group. Such pesticides include meta-aryloxy-benzyl esters of substituted cyclopropane-carboxylic acid and chlorophenyl-acetic acids which have outstanding insecticidal properties.
A possible route to the preparation of a meta-aryloxy-benzaldehyde is by the halogenation of the corresponding meta-aryloxy-toluene to form the benzyl halide, followed by conversion of that halide into the benzaldehyde. However, although this route is satisfactory in principle, it does suffer from certain drawbacks, namely (i) the need to control the conditions of the halogenation step to provide the maximum yield of benzyl halide at the expense of the overall yield of other halogenated products (e.g., benzal halide and ring-halogenated products) and (ii) the yield of benzyl halide rarely exceeds 70%.
It has now been found that these drawbacks can be minimized by the adoption of a modified process which enables mixtures of side-chain halogenated meta-aryloxy-toluenes, especially a mixture of the benzyl and benzal halides to be converted into the aldehyde.